Abstract: The present disclosure is directed to specimen processing assemblies including (a) a lower plate (10), (b) an upper plate (30) complementary to the lower plate, and (c) a chamber formed therefrom. In some embodiments, the formed chamber is adapted to perform an unmasking operation, e.g. antigen retrieval and/or target retrieval. In some embodiments, the specimen processing assemblies are configured to maintain a specimen-bearing substrate (15) horizontal during all processing steps. The present disclosure is also directed to systems including one or more independently operable specimen processing assemblies.